a) Field of the Invention
The present invention relates to an electronic musical instrument, and more particularly to an electronic musical instrument capable of electronically realizing a resonance effect of a natural musical instrument such as a piano which has a resonance mechanism of a plurality of resonance plates provided for piano strings.
b) Description of the Related Art
In a natural musical instrument piano, each key is provided with a string and a hammer. In response to a key depression, the hammer strikes the string to cause vibration of the string. Each string is provided with a damper. The damper detaches from the string when the key is depressed, and touches the string when the key is released. A piano has also a sustain pedal (damper pedal). When the sustain pedal is depressed, dampers of all keys detach from the strings. Therefore, when the sustain pedal is depressed, music sounds are maintained to be produced and do not attenuate for a long period even if keys are released.
When a key is depressed while the sustain pedal is depressed, the hammer strikes the string and the latter vibrates. This vibration transmits to other strings via a frame or the like. If transmitted vibration induce a resonance of another string, this string starts vibrating even if the string is not struck, and generates a resonance sound. It has been proposed to realize an electronic musical instrument capable of generating such resonance sounds.
A conventional resonance sound generator will be described with reference to FIG. 5. FIG. 5 is a block diagram showing the fundamental structure of a tone signal generator and a resonance signal generator of a conventional electronic musical instrument.
A tone signal generator 50 generates a tone signal having a pitch corresponding to a depressed key, and gives this tone signal a desired tone color and an amplitude envelope corresponding to the states of a key depression, a key release, and a sustain pedal. The tone signal generator 50 has a plurality of tone signal forming channels 51-1 to 51-n and an adder 52. When a key is depressed, one of the tone signal forming channels is assigned to this key by an unrepresented channel assignment means. If all the tone signal forming channels are generating tone signals and a new key is depressed, generation of a tone signal having a longest time lapse after the key release or a tone signal most attenuated is stopped and its channel is assigned to the newly depressed key. This process is generally called a truncate process.
An assigned tone signal forming channel 51-i generates a tone signal having a pitch corresponding to the depressed key.
Each tone signal forming channel 51-1 to 51-n is connected to the adder 52. The adder 52 adds tone signals supplied from the tone signal forming channels 51-1 to 51-n.
A resonance signal generator 60 generates m resonance signals having a different resonance frequency in accordance with an inputted tone signal, and adds a resonance signal to an original tone signal. The resonance signal generator 60 has m resonance signal forming channels 61-1 to 61-m and adders 65 and 66. Each resonance signal forming channel 61-1 to 61-m is supplied with a tone signal from the tone signal generator 50 and a sustain signal SUS from a sustain pedal switch 70. The sustain signal SUS takes a level "1" when the sustain pedal is depressed, and a level "0" when it is released.
Each resonance signal forming channel is a comb filter with a circulating signal path. This comb filter is constituted by an adder 62, a multiplier 63, and a delay circuit 64.
The adder 62 adds an output of the delay circuit 64 to a tone signal supplied from the tone signal generator, and outputs the result to the multiplier 63.
The multiplier 63 gives the tone signal supplied from the adder 62 a predetermined feedback gain, and supplies the result to the delay circuit 64. The feedback gain can be set to a desired value by an unrepresented control means. An output of the multiplier 63 is an output of each resonance signal forming channel, and is inputted to the adder 65. In addition to a tone signal from the adder 62, a sustain signal SUS from the sustain pedal switch 70 is supplied to the multiplier 63. When the sustain signal SUS is "1", i.e., when the sustain pedal is depressed, the multiplier 63 provides a preset feedback gain. When the sustain signal SUS is "0", i.e., when the sustain pedal is released, the feedback gain at the multiplier 63 becomes null so that an output of the resonance signal forming channel is null.
The delay circuit 64 delays a signal supplied from the multiplier by a predetermined time, and supplies it to the adder 62. The delay time can be set to a desired value by an unrepresented control means. By setting the delay time to a proper value, the resonance frequency of the comb filter can be set to a desired value.
By supplying a tone signal from the tone signal generator 50 to each resonance signal forming channel 61-1 to 61-m constructed as above, it becomes possible for each resonance signal forming channel 61-1 to 61-m to form a resonance signal having a specific resonance frequency.
The adder 65 adds the resonance signals supplied from the resonance signal forming channels 61-1 to 61-m, and supplies the result to the adder 66.
The adder 66 adds a tone signal supplied from the tone signal generator 50 to the resonance signal, and supplies the result to a sound system 67.
The sound system 67 converts a digital tone signal supplied from the resonance signal generator 60 into an analog signal and produces sounds containing resonance sounds.
With the resonance signal generator shown in FIG. 5, an effective resonance sound can be produced when the sustain pedal is pushed down. However, when the sustain pedal is released, a resonance sound is not produced. In a natural musical instrument such as a piano, there is a case that a plurality of keys are depressed at the same time in an ordinary music play. In such a case, dampers of the depressed keys detach from the strings so that resonances occur at these strings even if the damper pedal is not pushed down. With the conventional resonance signal generator shown in FIG. 5, however, even if a plurality of keys are depressed at the same time without depressing the sustain pedal, such resonance sounds are not generated.